1. Field of the Invention
Embodiments of this disclosure relate to devices for holding in a curved configuration or fitting metal plates into a cylindrical tank as the tank is being constructed. Embodiments may also be provided with means for removing from between metal plates the spacing shims used to hold the metal plates in the proper spaced apart relationship while they are being tacked or welded in place during the construction of a tank.
2. Description of the Related Art
Current technology for fitting horizontal weld seams in shop or field built tanks and vessels uses a manual system of shims, wedges, pins, key plates, bull pins, u-bars, leaf springs, hammers, and other accessories, some of which are tack welded or welded to the plates to be aligned. This system is very labor intensive, has high material cost, and is time consuming.
The construction of large cylindrical tanks involves first establishing a circular base onto which horizontal shell plates of metal are to be welded to create a tank. Once the base is established, the first horizontal row of metal shell plates are tacked or welded to the perimeter of the base so that the first horizontal row of metal plates are oriented perpendicular to the base and form a complete cylinder around the base.
Once the first row of shell plates has been welded in place, the fitting of subsequent rows of metal shell plates becomes more difficult since the metal plates now must be lifted upward and placed on top of the first row of welded plates. What makes this even more difficult is that the metal plates forming the second and subsequent rows on the tank must be flexed to fit the curvature or girth of the first row and must be spaced properly from the next lower row of plates so that they can be welded together. All of this is done above the base level and at an ever increasing height above the base level as the tank nears completion of its final height.
Generally, the vertical seams of the plates are welded together and then the horizontal seams of the plates are fitted and/or welded together. Shims are used to hold the plates in the proper spacing and alignment to be welded, but must be removed during the welding process.
Up until now, the flexing of the metal plates to align the new plates with the girth of the next lower row of plates has been accomplished manually. Likewise, the placement of shims to achieve the proper gap and alignment between plates for fitting and/or welding and the removal of those shims from between the plates has also been accomplished manually.
Currently there are automatic welding machines that automate the welding process for tanks, but there is still a need for an automated plate girth alignment and fitting device and for an automated shim removal device for removing shims as the plates are being welded.
Embodiments of this disclosure address these needs by providing a device or devices for aligning the new plates vertically with the girth of the plates of the next lower row on the tank. Optionally, the device can be provided with equipment for automatically removing shims from between the new plate and the plates of the next lower row as the welding process proceeds. This device can be a stand-alone piece of equipment or can be incorporated into an existing automatic girth welding machine that is designed for a tank welding operation.
These new devices are being developed to reduce labor input and material costs as well as to shorten the time required to perform plate alignment, while improving plate alignment accuracy and safety in horizontal weld seam fitting and welding operations.